Below is a example of the issue.

Create a Labs FileDialog and specify a filename to pre-populate and it will prepend a '/' to the name when the file dialog opens.

The ability to add a selected file is one of the main reasons to use the labs version in the first place so it would be really nice if this worked.

import QtQuick 2.10
import QtQuick.Window 2.10
import Qt.labs.platform 1.0

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")

    FileDialog {
        Component.onCompleted: open()

        fileMode: FileDialog.SaveFile

        currentFile: "export.csv"
    }
}